The present invention relates to a method and apparatus for the ultra-purification of chemicals for semiconductor processing. In particular, the present invention provides a purification process where a compressed fluid is partially condensed by expanding the fluid through an orifice or any other expansion means such as a capillary or the like.
In the manufacture of semiconductor devices, the industry requires high purity chemicals to avoid the introduction of defects into the device during various processing steps. Such processing steps include, among others, plasma etching, wet etching, and the like. The presence of impurities in the processing chemicals used in these processes often cause defects. In processing chemicals such as hydrochloric acid (HCl), chlorine gas (Cl.sub.2), nitrogen trifluoride (NF.sub.3), or the like, the impurities include metal contaminants (eg., Fe, Ni, Cr, Cu, Al, Mn, Zn, etc.), moisture (eg., H.sub.2 O), carbon dioxide (eg. CO.sub.2), and the like.
In ESG HCl, the predominant impurities are typically iron and moisture. When geometrically large enough, the impurities can, for example, short-out adjacent active structures within a device, and thus cause lower wafer yields (or die per wafer). Such impurities are known in the art as "particles." In addition, if the impurities are charged, the charged impurities are generally detrimental to the electrical characteristics of the device. Moreover, the impurities can also be corrosive to the device structure. As line widths for the state-of-art device become smaller (typically sub-micron), the industry demands high purity chemicals having lower impurity levels. In addition to the manufacture of semiconductors, the optical, aerospace, pharmaceutical industries, and the like also require high purity chemicals.
In the past, the semiconductor industry often used electronic semiconductor grade chemicals supplied in bottles. The bottles contain high purity chemicals also called electronic semiconductor grade (ESG) chemicals having purity levels of about 99.99% by weight or "four nine" purity. The bottles are also typically about 20 liters or less in size. However, the electronics industry is currently switching to chemicals in bulk on-site supplies. The use of ESG chemicals in bulk provides the manufacturer with lower chemical costs because bulk chemicals require less handling and have a lower cost per unit than bottled chemicals.
However, the change to bulk on-site supplies within the industry is not free from problems. For example, electronic semiconductor grade chemicals such as ESG HCl inherently possess moisture. The moisture causes severe corrosion in parts such as transport lines, bulk storage tanks, valves, pressure regulation devices, and pumps. Such parts are typically required for providing the chemicals in bulk on-site supplies. As the ESG HCl breaks down the parts, additional impurities are released into the chemical stream. Therefore, a typical maintenance program requires the periodic replacement of the parts to reduce the amount of impurities originating therefrom. The maintenance program also replaces the parts to lessen their failure rate. Since the parts often carry highly corrosive chemicals, the parts demand proper maintenance to prevent chronic failure, and thus reduce serious safety and/or environmental problems.
The semiconductor industry needs ultra-purified chemicals having low levels of impurities. To purify the chemicals, impurities are partially removed using a metal filter process. The metal filter process employs a filter having a certain amount of iron therein. The metal filter partially purifies HCl by filtering out a portion of the impurities on the small pores of the filter. However, because of iron in the filter material itself, the metal filter introduces increased levels of iron into the HCl. The increased level of iron in the HCl is detrimental to the manufacture of the semiconductor device. In addition, the corrosive nature of the HCl which attacks the filter material itself decreases filter efficiency and life. Decrease in filter life often leads to increased filter maintenance and thus higher costs in operating the metal filter process. Thus, the metal filter process fails to provide the ultra-purified HCl required for manufacturing the state-of-art device.
From the above, it is seen that an improved technique for generating high purity chemicals for the electronics industry is needed.